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What active solar radiation management (SRM) field tests are currently underway and who funds them?
Executive summary
Active field testing of active solar radiation management (SRM) is limited and small in scale: NOAA and a few research efforts have conducted atmospheric sampling flights and very small releases, while most recent funding has focused on modelling and lab work rather than large outdoor experiments [1] [2]. Major new philanthropic and government funding streams — notably the Simons Foundation’s SRM grants and the UK’s ARIA “climate cooling” awards — are financing laboratory, modelling and coordinated research programs, with explicit calls that could enable limited outdoor work; public-sector programmes remain the principal announced funders [3] [4] [5] [2] [6].
1. What counts as an “active SRM field test” — and why few exist
Researchers and regulators differentiate desk studies, lab experiments and modelling from “active” outdoor tests that intentionally alter radiation (e.g., tiny aerosol injections or marine cloud brightening trials). Government agencies have prioritized observation and modelling; NOAA’s program has supported aircraft sampling in the lower stratosphere and tracked a handful of small outdoor experiments, but large-scale purposeful SRM deployments are not underway in the public record [1]. The emphasis to date is on understanding processes and risks before doing anything at scale [4] [2].
2. Known small-scale or observational activities and who is tracking them
U.S. federal agencies have been the most explicit actors: NOAA received congressional direction to study activities that could change Earth’s radiation budget and has funded stratospheric aerosol process work and high-altitude sampling missions in coordination with NASA [1]. The U.S. EPA is tracking private actors and received notice about a start-up (“Make Sunsets”) claiming tiny SO2 balloon releases; EPA said Make Sunsets reported releasing about 0.1 tonnes of SO2 into the stratosphere as of May 2025 [1]. These are small, contested and under regulatory scrutiny rather than examples of large, funded experiments [1].
3. Who is funding SRM research (lab, modelling, governance) right now
Philanthropy has become a major funder: the Simons Foundation launched a targeted SRM program funding laboratory and theoretical work and hosted a roll‑out meeting of awardees; its calls allow budgets up to $500,000 per year and aim to fill basic scientific gaps [3] [4] [7]. National research councils and agencies are also investing: the UK’s Advanced Research and Invention Agency (ARIA) announced tens of millions for “climate cooling” projects (reported as ~£57M in UK announcements and described in coverage as a program with over $60M impact), and NERC funded new modelling projects with Cambridge, Exeter and Imperial teams [8] [2] [6]. NOAA remains the only U.S. federal agency explicitly funded to study SRM at scalewise levels referenced in available reporting [1].
4. What the new funding streams are paying for — and what they aren’t
Simons grants and ARIA-funded projects focus on laboratory studies, optical properties, climate-model impacts, and risk/impact assessment rather than open-air stratospheric spraying at scale; the Simons program explicitly funds lab and modelling work to probe uncertainties [3] [5]. NERC’s recent awards similarly fund modelling of four SRM approaches and public dialogue, not deployed field experiments [2]. GivingGreen and other policy analyses note donors often prefer research and governance capacity-building over direct experimentation [9]. In short, current major funds support risk-analysis, monitoring and basic science over large field deployments [4] [2] [6].
5. Disagreements and governance concerns to watch
There is active debate about whether increased funding should proceed: some scientists and funders argue better-funded research and modelling are needed to inform policy; critics warn SRM carries large environmental and social risks and urge governance first [4] [10] [11]. The npj Climate Action analysis highlights potentially large social costs and that funding pledges for governance and compensation mechanisms lag technical spending (less than $750M pledged for governance mechanisms as of Jan 2025 in one analysis) [10]. Policymakers and funders differ on whether small outdoor tests should go ahead while governance frameworks remain incomplete [2] [11].
6. Bottom line for readers seeking “active SRM field tests” now
Available reporting shows only a handful of small, contested releases and observational flights tracked by EPA/NOAA, while the bulk of new money (Simons, ARIA, NERC and other grants) is funding lab, model and governance work that could enable but does not yet equate to large-scale active field tests [1] [3] [2] [6]. If you want an up-to-date list of explicit outdoor trials, available sources do not list a sustained, large-scale field program funded and endorsed by major public agencies as of the cited reporting — instead they document funding flows into preparatory science and cautious monitoring [1] [4] [2].
If you want, I can pull the specific project lists from the Simons SRM awardees, ARIA grantee announcements, and the NERC-funded projects so you can see which groups and institutions are doing lab versus field work and who the principal investigators and funders are [3] [5] [2].